<!DOCTYPE html>
<html>

<head>
	<meta charset="utf-8" />
	<title>粒子漩涡特效</title>
	<style>
		html,
		body {
			margin: 0px;
			width: 100%;
			height: 100%;
			overflow: hidden;
			background: #000;
		}

		#canvas {
			position: absolute;
			width: 100%;
			height: 100%;
		}
	</style>
</head>

<body>
	<canvas id="canvas"></canvas>
	<script>
		function project3D(x, y, z, vars) {
			var p, d;
			x -= vars.camX;
			y -= vars.camY - 8;
			z -= vars.camZ;
			p = Math.atan2(x, z);
			d = Math.sqrt(x * x + z * z);
			x = Math.sin(p - vars.yaw) * d;
			z = Math.cos(p - vars.yaw) * d;
			p = Math.atan2(y, z);
			d = Math.sqrt(y * y + z * z);
			y = Math.sin(p - vars.pitch) * d;
			z = Math.cos(p - vars.pitch) * d;
			var rx1 = -1000;
			var ry1 = 1;
			var rx2 = 1000;
			var ry2 = 1;
			var rx3 = 0;
			var ry3 = 0;
			var rx4 = x;
			var ry4 = z;
			var uc = (ry4 - ry3) * (rx2 - rx1) - (rx4 - rx3) * (ry2 - ry1);
			var ua = ((rx4 - rx3) * (ry1 - ry3) - (ry4 - ry3) * (rx1 - rx3)) / uc;
			var ub = ((rx2 - rx1) * (ry1 - ry3) - (ry2 - ry1) * (rx1 - rx3)) / uc;
			if (!z) z = 0.000000001;
			if (ua > 0 && ua < 1 && ub > 0 && ub < 1) {
				return {
					x: vars.cx + (rx1 + ua * (rx2 - rx1)) * vars.scale,
					y: vars.cy + y / z * vars.scale,
					d: (x * x + y * y + z * z)
				};
			} else {
				return { d: -1 };
			}
		}
		function elevation(x, y, z) {
			var dist = Math.sqrt(x * x + y * y + z * z);
			if (dist && z / dist >= -1 && z / dist <= 1) return Math.acos(z / dist);
			return 0.00000001;
		}
		function rgb(col) {
			col += 0.000001;
			var r = parseInt((0.5 + Math.sin(col) * 0.5) * 16);
			var g = parseInt((0.5 + Math.cos(col) * 0.5) * 16);
			var b = parseInt((0.5 - Math.sin(col) * 0.5) * 16);
			return "#" + r.toString(16) + g.toString(16) + b.toString(16);
		}
		function interpolateColors(RGB1, RGB2, degree) {
			var w2 = degree;
			var w1 = 1 - w2;
			return [w1 * RGB1[0] + w2 * RGB2[0], w1 * RGB1[1] + w2 * RGB2[1], w1 * RGB1[2] + w2 * RGB2[2]];
		}
		function rgbArray(col) {
			col += 0.000001;
			var r = parseInt((0.5 + Math.sin(col) * 0.5) * 256);
			var g = parseInt((0.5 + Math.cos(col) * 0.5) * 256);
			var b = parseInt((0.5 - Math.sin(col) * 0.5) * 256);
			return [r, g, b];
		}
		function colorString(arr) {
			var r = parseInt(arr[0]);
			var g = parseInt(arr[1]);
			var b = parseInt(arr[2]);
			return "#" + ("0" + r.toString(16)).slice(-2) + ("0" + g.toString(16)).slice(-2) + ("0" + b.toString(16)).slice(-2);
		}
		function process(vars) {
			if (vars.points.length < vars.initParticles) for (var i = 0; i < 5; ++i) spawnParticle(vars);
			var p, d, t;
			p = Math.atan2(vars.camX, vars.camZ);
			d = Math.sqrt(vars.camX * vars.camX + vars.camZ * vars.camZ);
			d -= Math.sin(vars.frameNo / 80) / 25;
			t = Math.cos(vars.frameNo / 300) / 165;
			vars.camX = Math.sin(p + t) * d;
			vars.camZ = Math.cos(p + t) * d;
			vars.camY = -Math.sin(vars.frameNo / 220) * 15;
			vars.yaw = Math.PI + p + t;
			vars.pitch = elevation(vars.camX, vars.camZ, vars.camY) - Math.PI / 2;
			var t;
			for (var i = 0; i < vars.points.length; ++i) {
				x = vars.points[i].x;
				y = vars.points[i].y;
				z = vars.points[i].z;
				d = Math.sqrt(x * x + z * z) / 1.0075;
				t = .1 / (1 + d * d / 5);
				p = Math.atan2(x, z) + t;
				vars.points[i].x = Math.sin(p) * d;
				vars.points[i].z = Math.cos(p) * d;
				vars.points[i].y += vars.points[i].vy * t * ((Math.sqrt(vars.distributionRadius) - d) * 2);
				if (vars.points[i].y > vars.vortexHeight / 2 || d < .25) {
					vars.points.splice(i, 1);
					spawnParticle(vars);
				}
			}
		}
		function drawFloor(vars) {
			var x, y, z, d, point, a;
			for (var i = -25; i <= 25; i += 1) {
				for (var j = -25; j <= 25; j += 1) {
					x = i * 2;
					z = j * 2;
					y = vars.floor;
					d = Math.sqrt(x * x + z * z);
					point = project3D(x, y - d * d / 85, z, vars);
					if (point.d != -1) {
						size = 1 + 15000 / (1 + point.d);
						a = 0.15 - Math.pow(d / 50, 4) * 0.15;
						if (a > 0) {
							vars.ctx.fillStyle = colorString(interpolateColors(rgbArray(d / 26 - vars.frameNo / 40), [0, 128, 32], .5 + Math.sin(d / 6 - vars.frameNo / 8) / 2));
							vars.ctx.globalAlpha = a;
							vars.ctx.fillRect(point.x - size / 2, point.y - size / 2, size, size);
						}
					}
				}
			}
			vars.ctx.fillStyle = "#82f";
			for (var i = -25; i <= 25; i += 1) {
				for (var j = -25; j <= 25; j += 1) {
					x = i * 2;
					z = j * 2;
					y = -vars.floor;
					d = Math.sqrt(x * x + z * z);
					point = project3D(x, y + d * d / 85, z, vars);
					if (point.d != -1) {
						size = 1 + 15000 / (1 + point.d);
						a = 0.15 - Math.pow(d / 50, 4) * 0.15;
						if (a > 0) {
							vars.ctx.fillStyle = colorString(interpolateColors(rgbArray(-d / 26 - vars.frameNo / 40), [32, 0, 128], .5 + Math.sin(-d / 6 - vars.frameNo / 8) / 2));
							vars.ctx.globalAlpha = a;
							vars.ctx.fillRect(point.x - size / 2, point.y - size / 2, size, size);
						}
					}
				}
			}
		}
		function sortFunction(a, b) {
			return b.dist - a.dist;
		}
		function draw(vars) {
			vars.ctx.globalAlpha = .15;
			vars.ctx.fillStyle = "#000";
			vars.ctx.fillRect(0, 0, canvas.width, canvas.height);
			drawFloor(vars);
			var point, x, y, z, a;
			for (var i = 0; i < vars.points.length; ++i) {
				x = vars.points[i].x;
				y = vars.points[i].y;
				z = vars.points[i].z;
				point = project3D(x, y, z, vars);
				if (point.d != -1) {
					vars.points[i].dist = point.d;
					size = 1 + vars.points[i].radius / (1 + point.d);
					d = Math.abs(vars.points[i].y);
					a = .8 - Math.pow(d / (vars.vortexHeight / 2), 1000) * .8;
					vars.ctx.globalAlpha = a >= 0 && a <= 1 ? a : 0;
					vars.ctx.fillStyle = rgb(vars.points[i].color);
					if (point.x > -1 && point.x < vars.canvas.width && point.y > -1 && point.y < vars.canvas.height) vars.ctx.fillRect(point.x - size / 2, point.y - size / 2, size, size);
				}
			}
			vars.points.sort(sortFunction);
		}
		function spawnParticle(vars) {
			var p, ls;
			pt = {};
			p = Math.PI * 2 * Math.random();
			ls = Math.sqrt(Math.random() * vars.distributionRadius);
			pt.x = Math.sin(p) * ls;
			pt.y = -vars.vortexHeight / 2;
			pt.vy = vars.initV / 20 + Math.random() * vars.initV;
			pt.z = Math.cos(p) * ls;
			pt.radius = 200 + 800 * Math.random();
			pt.color = pt.radius / 1000 + vars.frameNo / 250;
			vars.points.push(pt);
		}
		function frame(vars) {
			if (vars === undefined) {
				var vars = {};
				vars.canvas = document.querySelector("canvas");
				vars.ctx = vars.canvas.getContext("2d");
				vars.canvas.width = document.body.clientWidth;
				vars.canvas.height = document.body.clientHeight;
				window.addEventListener("resize", function () {
					vars.canvas.width = document.body.clientWidth;
					vars.canvas.height = document.body.clientHeight;
					vars.cx = vars.canvas.width / 2;
					vars.cy = vars.canvas.height / 2;
				}, true);
				vars.frameNo = 0;
				vars.camX = 0;
				vars.camY = 0;
				vars.camZ = -14;
				vars.pitch = elevation(vars.camX, vars.camZ, vars.camY) - Math.PI / 2;
				vars.yaw = 0;
				vars.cx = vars.canvas.width / 2;
				vars.cy = vars.canvas.height / 2;
				vars.bounding = 10;
				vars.scale = 500;
				vars.floor = 26.5;
				vars.points = [];
				vars.initParticles = 700;
				vars.initV = .01;
				vars.distributionRadius = 800;
				vars.vortexHeight = 25;
			}
			vars.frameNo++;
			requestAnimationFrame(function () {
				frame(vars);
			});
			process(vars);
			draw(vars);
		}
		frame();
	</script>
</body>

</html>